By charging fees for services previously included in the full price of economy tickets, Frontier said it has cut its lowest fares by an average of 12%. Above, Frontier planes at Denver International Airport in 2010.

By charging fees for services previously included in the full price of economy tickets, Frontier said it has cut its lowest fares by an average of 12%. Above, Frontier planes at Denver International Airport in 2010. (David Zalubowski, AP)

Hugo MartÃ­n

With new passenger fees, Frontier Airlines took another step Monday in its shift toward refocusing itself as an ultra-low-cost carrier.

Starting Monday, Frontier began to charge passengers $20 to $50 to carry on a bag and $3 to $15 to preselect a seat. In the past, Frontier waived both fees for economy fliers who booked through Flyfrontier.com. Now, all economy fliers pay the fee.

For more than a year, the Denver carrier has been moving toward the business model honed by Spirit Airlines and Allegiant Airlines, both of which charge for carry-on bags and dozens of other services.

The shift gained pace last year when Indigo Partners bought Frontier from Republic Airways Holdings Inc. for $36 million in cash. Indigo also agreed to accept $109 million in debt. Indigo helped finance Spirit Airlines, making it the airline with the highest profit margin in the nation last year.

Last week, Frontier announced the appointment of a new president, Barry L. Biffle, who previously worked as executive vice president at Spirit and as chief executive at VivaColombia, the first ultra-low-cost carrier in South America. He will take his post in July.

A list of the nearly 30 fee categories at Frontier includes a $5 fee to print out a paper receipt and $10 to make a reservation over the phone.

By charging fees for services previously included in the full price of economy tickets, Frontier said it has cut its lowest fares an average of 12%.

"With an unbundled product, customers can save even more by choosing to pay for only the products that they want, allowing them to customize their flight experience for each and every flight," said Frontier Chief Executive David Siegel.